71 GMC lights and blinker problem need help

[mttnlsn]

I am working on a 71 gmc 3/4 ton 2x4. My problem is when the head lights are OFF my blinkers work correctly. When my blinkers are off my head lights work correctly. When my headlights are on and I try my blinkers my dash board lights blink, the blinker arrows are lit up. When I switch from hi to low beam half my dash board lights go out all together? If I turn my light dimmers down all the way the blinkers work better, but not perfect. I have installed a new light switch and blinker wiring harness in the column. Any ideas?? This is killing me. I hate electrical problems. Thanks for the help. This is my first post.